Field of Invention
Various embodiments of the present invention relate to a semiconductor memory device, and more particularly, to a 3D semiconductor memory device.
Description of Related Art
In general, a semiconductor memory device is formed in a 2D structure in which memory cells are formed on a substrate in a single layer. The 2D semiconductor memory device improves integration of the memory cells by decreasing a flat surface are occupied by each of the memory cells by a micro pattern forming technology.
As the technology of improving integration of the 2D semiconductor memory device reaches the limit, a 3D semiconductor memory device, in which memory cells are stacked on a substrate in a form of multi layers, has been suggested. Even though the flat surface area occupied by each of the memory cells is not decreased, the 3D semiconductor memory device may improve integration of the memory cells. Researches and development are required in various aspects in order to commercialize the 3D semiconductor memory device.